In many parts of the United States, rainfall is insufficient and/or too irregular to keep turf and landscaping green and therefore irrigation systems are installed. Such systems typically include a plurality of underground pipes connected to sprinklers and valves, the latter being controlled by an electronic irrigation controller. One of the most popular types of sprinklers is a pop-up rotor-type sprinkler. In this type of sprinkler a tubular riser is normally retracted into an outer cylindrical case by a coil spring. The case is buried in the ground and when pressurized water is fed to the sprinkler the riser extends. A turbine and a gear train reduction are mounted in the riser for rotating a nozzle turret at the top of the riser. The gear train reduction is often encased in its own housing and is often referred to as a gear box. A reversing mechanism is also normally mounted in the riser along with an arc adjustment mechanism.
Oscillating rotor-type sprinklers with adjustable arc limits have been used extensively. Typically they have used a reversing mechanism with four pinion gears meshed together and mounted between upper and lower arc-shaped frames. One of the inner pinion gears is driven by the gear reduction mechanism. The frames rock back and forth with the aid of over-center springs and pinion gears on opposite ends of the frames alternately engage a bull gear. The main drawback of this design is that the pinion gears are held in engagement with the bull gears with a relatively weak spring force, which limits the amount of torque that can be applied to rotate the nozzle. One type of gear driven rotor-type sprinkler incorporates a planetary gear drive that includes at least a portion of the reversing mechanism. See U.S. Pat. No. 7,677,469, of Michael L. Clark granted Mar. 16, 2010, entitled “Sprinkler with Reversing Planetary Gear Drive.” The advantage of including at least a portion of the overall reversing mechanism in the planetary gear drive is that the shifting can be done in a low torque region of the drive where damage and wear to gears is much less likely to occur.